Thermostat inoperable below freezing temps

[IdahoBob]

On occasion, we have a need to turn on our trailer's furnace when the interior temperature is less than freezing. We had an aftermarket Honeywell digital thermostat in our prior rig and it would not operate at temperatures below freezing. So during the winter, I removed it (it just un-snapped from its mounting bracket) and kept it "warm" until we needed it. No problem.

Our current rig has a 'Coleman Mach RVComfort.HC" digital thermostat, that, Coleman confirms, will also not operate at temps below freezing. But it is hard wired into the trailer and not easy/practical to remove (to keep it warm). The factory rep suggested that one merely has to jumper the red wire to the white wire to turn on the furnace. I'm cogitating on a good way to do that.

Have you ever had trouble turning on your furnace when the interior of your rig was less than freezing?

Bob

[SKP Kirk]

Not only have I never heard of that, I am suspicious of the claim that it is normal! I would contact the manufacturer to ask if that is true. As a retired service tech I have great difficulty in believing that the tech knows. I have a Suburban thermostat in the present RV and had one from Dometic in the previous and I have never had any problem turning on heat when it is below freezing.

[IdahoBob]

Originally Posted by SKP Kirk

Not only have I never heard of that, I am suspicious of the claim that it is normal! I would contact the manufacturer to ask if that is true. As a retired service tech I have great difficulty in believing that the tech knows. I have a Suburban thermostat in the present RV and had one from Dometic in the previous and I have never had any problem turning on heat when it is below freezing.

SKP Kirk,

I reread my post and don't see that I made a claim that this reported thermostat limitation is "normal". I am just reporting what the makers of the thermostats say. It would be surprising if they would undersell their products.

I think this reported issue pertains only to digital thermostats. Is your experience with digital thermostats? And have you actually used your thermostats when the interior temperature of your rig in below freezing?

If so, that is encouraging to me.

Bob

[SKP Kirk]

Bob, I apologize as it was not you that I was questioning, but rather whoever it was at Coleman who said it was not able to operate when temperatures are below freezing. I should have been more clear in how I responded, but my words don't always come out quite the way I intended!

What I am saying is that as a retired electrical/electronic tech I can see no reason for the design to not work at below freezing temperatures and I believe that someone is trying to sell you a bill of goods.

Yes, I have gone out to the RV and started the furnace in our previous motorhome with the Dometic thermostat with temperatures well below freezing as it was winterized at the time. Our present RV has a Suburban thermostat which I did that same thing this past winter when preparing the RV for a winter trip. It had no heat inside until I turned on the furnace as the water lines were all blown out at the time and the water heater was drained.

The Dometic thermostat in our previous motorhome was one of the solid state circuit board designs and controlled both the air conditioner and the furnace. The Suburban that I now have is of a basic design as it only controls the furnace and is of a very simple design so may be a different animal entirely. I just took the cover off to look at the Suburban, and it borders on primitive... It isn't digital at all, as I had previously assumed.

[IdahoBob]

Kirk,

Thank you for your clarification. I too am a little bit suspicious of an intentional (or magical) shutdown at 32 degF. But in my situation, if that should happen, it would be a major inconvenience. So I am in the process of installing a miniature Radio Shack slider switch underneath the cover of the thermostat. That switch, when activated, will bypass the thermostat circuitry and connect 12vdc directly to the furnace control relay.

I should know early this coming January if my thermostat does or does not shut down at below freezing temps. If I can remember that far from now, I will post my "findings".

Bob

[oh oh]

Bob
I have had mine down to 15 and never had a problem. We got the same trailer.

Cal

[IdahoBob]

Originally Posted by oh oh

Bob
I have had mine down to 15 and never had a problem. We got the same trailer.

Cal

Thanks Cal! Good news for me! Was that 15 F inside the trailer?

Bob

[oh oh]

That was outside and inside last winter going south in Id and Ut

[Skip426]

Originally Posted by IdahoBob

The factory rep suggested that one merely has to jumper the red wire to the white wire to turn on the furnace. I'm cogitating on a good way to do that.
Bob

I wouldn't start without at wiring schematic of the t'stat and the furnace.
Because powering up the wrong wire could burn up the control board in the furnace.

[IdahoBob]

Originally Posted by oh oh

That was outside and inside last winter going south in Id and Ut

Thanks Cal.

[IdahoBob]

Originally Posted by Skip426

I wouldn't start without at wiring schematic of the t'stat and the furnace.
Because powering up the wrong wire could burn up the control board in the furnace.

I did that and the switch works as planned. Now, armed with this spectacular success, I am looking for a very tiny LED light to illuminate the display (to assist our tired old eyes).

Bob

[RVGuy1966]

I would think its possible to install a timer switch that will keep a set of contacts closed for about 10 minutes or whatever time is needed to run the furnace for enough time to bring it above freezing. put the switch next to the thermostat and in the below freezing situations you can just press the button and when the temp gets above freezing the thermostat will take over.....


not sure why this is a problem as most TT aren't designed for deep winter living....if you stay in one for too long in winter temps the condensation that builds up can destroy the walls.....


or so I read.......

[IdahoBob]

Originally Posted by RVGuy1966

I would think its possible to install a timer switch that will keep a set of contacts closed for about 10 minutes or whatever time is needed to run the furnace for enough time to bring it above freezing. put the switch next to the thermostat and in the below freezing situations you can just press the button and when the temp gets above freezing the thermostat will take over.....
.

An excellent idea. Since we will rarely need this switch (if ever, per this thread ), I opted to put an "on/off" slide switch inside the thermostat's housing. I should know if it is needed early next January.

Bob